The invention relates to valves, especially those suitable for HVAC applications, and mechanisms enabling adjustment of flow in the field. In particular, the invention provides mechanisms for use with valve actuators and control valves to enable field adjustment. In the preferred forms, the valves are of the pressure independent and characterized flow variety.
In HVAC plants, water distribution can be accomplished at constant or variable flow. Each type of distribution system has advantages and disadvantages. Today, variable flow systems using electronic 2-way control valves have become generally accepted as the industry standard due to their benefits, mainly reduced pumping cost achieved as a result of reducing pump head and flow. In addition, this type of system enables plants to be designed with a diversity factor because flow is only needed where energy is demanded. However, these systems are not without their disadvantages.
A very significant disadvantage with most systems in place today is that balancing the system is a very time consuming and costly effort. According to a flow design for typical systems, each control valve requires a balancing valve to adjust the hydronic circuit. The balancing procedure dictates the quality of the system and requires highly skilled technicians and tools. During the balancing, all control valves must be in their open position. However, as soon as the system is running, depending on different cooling or heating load requirements in the building, valves are permanently closing and opening which results in a dynamically changing system pressure. Balancing variable flow systems is time consuming and can be conducted only under “static” design conditions.
If terminals are added to a typical conventional system, the whole system needs to be rebalanced because some existing terminals must be throttled back. This is especially a problem where floors are periodically remodeled for new or existing tenants and the uses vary with each remodeling. Wherever the uses change, balancing of the whole system is required. Moreover, typically a building is running under design conditions only 1% of the time. The other 99%, the hydronic system needs to provide an average load of 50%. Thus, flow is reduced to 20%, and differential pressures across control valves increase. Since the CV-rating of the valve is typically sized for design conditions, the valve authority decreases and the modulating valve is downgraded to one acting open or close only. This makes hunting expected.
Control circuits are interactive. Therefore, when one control valve closes, the differential pressures on other circuits increases and the associated control valves must close to compensate. So when one or more loops become instable, control problems can spread to other control valves.
In typical current systems, if flow is higher than required, ΔT will decrease and result in a cooling plant with lower return temperatures to the chiller and reduce the efficiency. If one chiller cannot run at peak efficiency, it is more likely that the next chiller in a series will be forced to start sooner than required causing additional electricity and maintenance costs. The opposite happens in a condensing boiler where a higher return temperature can avoid the condensing process when the dew point of the exhaust gases cannot be achieved. The same phenomenon can happen in coils. In a heating coil for instance, overflow will result in a lower ΔT and decrease the coil's performance which can result in discomfort due too a low room temperature.
Significant developments in HVAC valves have been made in the recent past with the provision of characterized valves, in general, and particularly of the pressure independent variety. Because of these improvements the disadvantages of variable flow systems are largely eliminated for most HVAC-applications. The valves now available for HVAC applications include characterized openings where the degree of opening movement is proportional to flow rate. In U.S. Pat. No. 6,039,304, Carlson, et al., describes a ball valve with modified characteristics. The valve includes a disk for characterizing flow to permit a proportional opening of the valve to correspond to a predetermined flow rate. These valves can provide essentially “equal percent” characteristics, although other flow characteristics may be desired and achieved and are commercially under the identifier of CCV. They employ a disk that includes a shaped opening and has one side shaped to interface with and conform to the shape of the exterior of the ball or plug. The disk fits inside the port at the seat area, and is secured by a ring. The ability of a valve to provide a flow rate proportional to the movement of a valve actuator is of great advantage when manufacturing and installing both valves and the actuators. In many tests and surveys the CCV has outperformed globe valves due to true equal-percentage valve characteristic and higher close-off ratings.
It is also important for HVAC and other applications that control valves have the ability to maintain a constant flow rate despite pressure fluctuations in the system. Valves having this capability are now available. For example, in U.S. Pat. No. 6,827,100, to Carlson, there is described a pressure independent control valve, which enables an HVAC operator to set flow rates for any of a plurality of zones and have the selected rates remain constant independent of variations in pressure due to variations in heat transfer demand in the several zones. These valves are commercially available under the identifier of PICCV. This capability is the most important at part-load; for instance, when a PICCV with a nominal flow of 10 GPM operates at 3 GPM, a flow of 3 GPM is maintained. These valves are made in number of sizes; however, not all rated flow rates can be made practically. Where exact flow rates are necessary at levels between the available sizes, it is necessary to program an actuator to supply the desired percentage of the required flow rate. In a PICCV the CCV is combined with a differential pressure regulator. This regulator maintains a constant flow passing through the valve regardless of pressure variations in the system.
Actuators for control valves are typically set at the factory and can be modified upon installation to provide a desired maximum flow rate. The closed position is typically offset past the zero point by a preset amount to achieve a high close off rating. As with all high close-off valves that employ a ball in their design, the ball passes well into the seat when rotated to the actuator's zero-degree position. Therefore, there is an amount of travel within the first degrees of ball rotation that passes back over this seat. For an actuator having a 90° turn arc from full off to full on, it is typical for this offset to be as much as 12° or more, or about 13% of the travel of the actuator. This offset provides an unacceptable delay in some circuits.
Among actuators of wide use in HVAC applications are those are those available from Belimo Aircontrols USA as LR24-3 US, series actuators, which provide a 100 second run time, provide a 90° movement and employ an overload sensor to stop movement when the voltage exceeds a predetermined value. Also available are a series of advanced actuators available from Belimo Aircontrols USA as MFT actuators, which include the ability to be preset to a limited range of movement. These actuators comprise electric motors with electronic control circuitry which is programmed to utilize a 2-10 Volt control signal to provide a designated angle of movement over a 100 second running time. The MFT actuators include controllers for providing feedback control signals. On floating point actuators, the running time is constant but dependent on the overall angle of rotation. They will run for the full 100 second running time unless an overload due stopped travel is sensed and used as a signal to shut off the motor. The actuators are electronic and are programmed using a special piece of equipment or a software tool. Field adjustments are not a simple matter.
There is a present need for means having the capability of simple and effective field adjustment of control valves to adjust valves to achieve desired flow rates of less than the design value of the valves. In particular, there is a need to provide field adjustment capability for control valves that are fully characterized and are designed to be opened by control movements proportional to flow rate independent of pressure, the field adjustment preferably being by a simple mechanical adjustment with a readily available hand tool.